Pressure fluid control system and valve



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ATTORNEY PRESSURE FLUID C'ONTRQL SYSTEM AND VALVE Robert D. Krehbiel,Hutchinson, Kane, assignor to Cessna Aircraft Company, Wichita, Karts, acorporation of Kansas Filed Feb. 19, 1959, 'Ser. No. 794,315

9 Claims. (Cl. 137---622) This invention relates to a control system fordouble acting hydraulic motors, whether or not the major components aregrouped in a single housing, as well as to a unitary valve in which theessential components of the control are grouped in a single housing.

More particularly the invention relates to a system and valve forcontrolling the flow of fluid under pressure to and from a double actinghoist cylinder, such as a cylinder used to raise and lower the boom of apower shovel, in which a very appreciable inertia force is built upduring fast lowering or dropping of the boom.

Under such condition of use, when a conventional con- .trol valve ismoved to a position in which the flow of fluid-to and from the doubleacting cylinder is blocked in order to stop the downward travel of theboom, inertia forces in the boom and the load it carries cause excessivepressure to build up in that end of the cylinder from which the returnof fluid to the system reservoir is blocked. Such excessive pressurecauses hammer and often causes a'break in some part of the-system.

It is an important object of this invention to eliminate the abovedescribed difficulty by providing a means incorporated in the controlsystem which affords relief of excess pressure when flow of fluid to andfrom the hydraulic motor is suddenly stopped by a control valve, suchpressure relief also affording a slight further movement of the cylinderplunger and of the controlled boom or other controlled element, and thusproviding a cushioned stop in the downward movement of the element.

Since the slightest movement of the plunger in a cylinder forces somefluid out one end of the cylinder, there must be an equivalent inflow offluid into the other end of the cylinder else cavitation or fluidstarving occurs in the cylinder. Consequently it is an additionalimportant object of the invention to eliminate cavitation by providingan associated means which affords flow of the necessary amount of fluidinto the cylinder to compensate for the slight cushioned movement of theplunger after 'flow of fluid to and from the cylinder'through the normalsupply and return passages has been blocked by the fluid control valve.

It is an additional object of the invention to provide 'a unitary fluidcontrol valve which incorporates the above described features.

Other objects and advantages of the invention will be apparent when thefollowing description is read in con 'nection with the accompanyingdrawing.

The single drawing figure is a schematic view of a hydraulic systemincluding a double acting motor for actuating the boom of a powershovel, my invention being embodied therein in the form of a unitarycontrol valve, shown in longitudinal vertical central section.

While the valve shown in the drawing is specifically designed forcooperative association with other valves in a multiple valve bank, andconsequently includes a socalled zig-zag type neutral by-pass passage10-41 through which fluid may continuously flow from the pump discharge:backto'the reservoir when there is no demand on States Patent 2 thesystem, it will be understood by those "familiar with this art that theinvention described hereincan be "embodied in unitary valves designed'tofunction independent of any association With other valves in a multiplebank.

Excepting the fluid flow control means shown in the drawing, thehydraulic system shown is considered 'conventional. A pump 12 issupplied with fluid from a reservoir 13 through a conduit 14 anddelivers that fluid at an increased pressure through a relief valve 15to a pressure fluid passage 16 in the body 17 of the "flow controlvalve.

Under selective control by a shiftable valve spool 18 pressure fluid maybe delivered from the supply passage 16 to either end of a double actingWorking cylinder 19 through motor ports 20 and 21 and lines 22 and 23,respectively, while fluid is simultaneously returned from the other endof the cylinder through the valve body, out througha return passage 24,into return line 25, and

Generally, my invention includes 'a fluid supply means 16; a fluidreturn means 2425; means forming two circuit control passages 26 and 27,connectible respectively to opposite sides .of 'a double acting motor19; a shiftable valve means 13 which has a neutral position in whichflow of fluid to and from both circuit control passage is blocked, andwhich is capable of selectively connecting either circuit .controlpassage with the fluid supply means '16 whileconnecting the othercircuit control pas sage with the fluid return means 24; twoseparatebypass passages 28 and 29 both openly communicating with the fluidreturn means 24, and each associated with and connectible to arespective one of the circuit control passages independent of theshiftable valve spool 18; and directional valves 30 and 31, one in eachof said 'by-pass passages, each directional valve beingshiftable to openin response'to differential pressure, the one valve 30 being oriented toafford flow of fluid from its associated circuit control passage '26into its associated by-pass passage 28 and thence to the fluid returnmeans 24, and the other directional valve 31 oriented to atford flowfrom the fluid return means 24 through its associated by-pass passage 29into the associated circuit control passage 27.

More specifically the valve illustrated, which embodies my controlsystem, includes a housing 17 which has a longitudinal valve spoolreceiving bore 32. This bore is intersected by two cooperating branches10 and 11 of a neutral by-pass passage, and bytwo separated butcommunicating fluid pressure supply ducts 33 and 34 which are deliveredfluid from a fluid pressure supply passage 16 through a ball check valve35. Bore 32 is also intersected by two circuit control passages 26 and27, each located adjacent a respective one of the supply ducts 33 and34, and by two by-pass passages 28 and 29,'each located adjacent arespective one of the circuit control passages 26 and 27. 1

The two circuit control passages 26 and '27 communicate respectivelywith motor ports 20 and 21, which in turn are connected by means ofconduits 22 and 23 to opposite ends of a hydraulic motor or doubleacting cylinder 19.

In the system illustrated, by-pass passage 28 functions as a'circuitrelief passage, while by-pass passage 29 functions as ananti-cavitation passage.

From the drawing it will be seen that the upper end of by-pass passage29 communicates directly with return passage 24. In the preferred formof valve shown the upper end of bypass passage 28 also communicates with0nd return passage 39, which would communicate di- 3 rectly with theupper end of passage 28 as well as with return line 25.

From the drawing it will be noted that passages 28 and 26 areintersected and connected by a cross bore 40 and that a directionalrelief valve assembly 30 is sealed in this cross bore to afford flow offluid under excessive pressure from passage 26 into passage 28.

The particular relief valve shown is pilot operated, although othertypes of pressure relief valves will serve the purpose of my inventionprovided the valve used opens only at a pressure greater than the normaloperating pressure existing in control passage 26 during the raising andlowering of the boom 41 by cylinder 19. Although the specific reliefvalve construction shown is not essential to theoperation of theinvention described in this application, and is disclosed completely andin greater detail in a separate patent application, it will be brieflydescribed to assure that the operation of my invention is clearlyunderstood.

Valve assembly 30 includes a housing 42 having a longitudinal bore 43extending part Way through the housing from its inner end. A valve seatinsert 44 is fixed in the inner end of bore 43. The housing has an inlet45 which communicates with chamber 26, and has an outlet 46 whichcommunicates with by-pass passage 28. A longitudinally bored valve head47 is reciprocable in bore 43 and is normally maintained on seat 44 by aspring 48, which bears against an orifice plate 49 and against acombination pilot valve seat and spring tension adjusting member 50. Aspring pressed pilot valve 51 is normally maintained seated on seat 50by a spring 52. The oper- .ation of this relief valve will be describedalong with the description of the operation of my complete controlsystem.

In the control valve illustrated the lower portions of passages 27 and29 are connected by an intersecting cross bore 53 in which is sealed adifferential pressure opened directional valve in the form of a simplecheck valve assembly 31. This includes a housing 54 having an inlet 55,a valve seat 56, a ball check 57, an outlet 58 forming a ball cage, anda fixed cross pin 59 to hold the ball in its cage.

To control fluid flow through the housing a shiftable valve means in theform of a cannelured valve spool 18 is reciprocably mounted in the bore32 of the housing. The spool is urged toward the neutral or centeredposition shown in the drawing by a conventional spring centeringassembly designated as a whole by the numeral 60.

The lands and grooves of spool 18 are so located that when the spool isin its neutral position communication between the fluid pressure supplymeans 16 and both circuit control passages 26 and 27 is blocked.Likewise communication is blocked between both circuit control passagesand the respective by-pass passages 28 and 29, and hence no fluid can bereturned through spool bore 32 into the'return means 24. During normaloperation this condition will positively lock the plunger in cylinder 19against movement in either direction, thus holding boom 41 in a'desiredposition.

Operation It will be understood that pressure of fluid in circuit reliefpassage 28 is relatively low because it communicates only with the fluidreturn side of the system.

When boom 41 is in the raised position shown and the operator desires tolower or drop it, he moves spool l8 to the left. Pressure fluid flowsfrom passage 16 past ball check 35, thru duct 34, bore 32, controlpassage 27, line 23 and into the inner end of cylinder 19 causing theplunger therein to move outward rapidly. As boom 41 drops fluid from theouter end of the cylinder 19 flows thru line 22, control passage 26,bore 32, transfer duct 36 and out thru return passage 24.

When the operator desires to stop the downward travel of the boom 41 hereturns spool 18 to its neutral position,

as shown in the drawing. This stops the normal flow of fluid from thesupply means 16 to the inner end of the cylinder 19 and also stops theflow of return fluid from the outer end of cylinder 19 back to thereturn passage 24. Ordinarily, due to the inertia forces built up duringthe downward travel of boom 41 the boom would come to an abrupt andcomplete stop which would result in an extreme pressure being built upin circuit control passage 26, and a resulting hammer throughout theentire hydraulic system shown. Such pressure and hammer could easilydamage various parts of the system.

With my invention, however, as the excess pressure builds up in controlpassage 26 fluid passes through orifice 61 into the bore in valve seat50, lifts pilot valve 51 off its seat, flows through bore 62 in valvehead 47 and into circuit relief passage 28. As fluid flows past thepilot valve 51 there is a resulting pressure drop in chamber 63 of thecircuit relief valve 30, and valve head 47 moves to the right in thedrawing against the pressure of spring 48. Thereafter fluid may flowfrom the lower portion of circuit control passage 26 through inlet 45and around the valve head 47 and out through the valve seat 44 intopassage 28, and thence to the return passage 24. As soon as a sufficientamount of fluid has escaped from control passage 26 to lower thepressure therein below the pressure at which the relief valve is set toopen, valve head 47 again moves to the left and seats under the urgingof spring 48. It will be understood that only a very minor amount ofliquid actually flows through the relief valve.

As a result of the escape of this small amount of fluid from controlpassage 26, however, the plunger in cylinder 19 is not brought to animmediate and complete stop. The escape of fluid first slows and thenstops the plunger travel and results in what is commonly termed acushioned stop, which completely eliminates the hammer which normallyaccompanies the stopping of a plunger which is being subjected at thetime to inertia forces.

During the described cushioned stop the plunger moves slightly incylinder 19, creating a partial vacuum in the inner end of the cylinder,in line 23, and in circuit control passage 27, because this circuit isunable to obtain supply fluid from the duct 34. As a result of the dropin pressure in control passage 27 the pressure in anti-cavitationpassage 29 causes fluid to flow from the return line through thatpassage past ball check 57 and thence through line 23 to the inner endof cylinder 19, thus preifllenting that end of the cylinder from beingstarved of uid.

It is believed that those familiar with this art will understand that byshifting spool 18 to the right of its neutral position, shown in thedrawing, supply fluid will pass from supply passage 16 through duct 33,bore 32, control passage 26, line 22 and into the outer end of cylinder19. Simultaneously fluid will return from the inner end of cylinder 19through line 23, circuit control passage 27, bore 32 and into returnpassage 24.

Having described the invention with sufficient clarity to enable thosefamiliar with this art to construct and use it, I claim:

1. A pressure fluid control system for a double acting fluid motorcomprising: fluid supply and fluid return means; means forming twocircuit control passages connected respectively to opposite sides ofsaid motor; shiftable valve means for selectively connecting eithercircuit control passage with the fluid supply means while connecting theother circuit control passage with the fluid return means, and in oneposition for blocking flow of fluid to and from said circuit controlpassages; means openly communicating with the fluid return means andforming two separate by-pass passages, each associated with andconnectible to a respective one of said circuit control passagesindependent of the shiftable valve means; and means responsive to anappreciable pressure fluid" motor comprising: fluid supply and fluid;re--- turn means; means forming two circuit control passages connectedrespectively to opposite sides of said motor; shiftable valve means forselectively connecting either circuit control passage with the fluidsupply means while connecting the other circuit control passage with thefluid return means, and in one position for blocking flow of fluid toand from said circuit control passages; means openly communicating withthe fluid return means and forming two separate by-pass'passages, eachassociated with and connectible' to a respective one of said circuitcontrol passages independent of the shiftable valve means: and'meansresponsive to an appreciable pressure increase inone circuit controlpassage and a pressure decrease in the other circuit control passage tobypass excess fluid from the higher pressure circuit control passagethrough its associated by-pass passage to the fluid return means, and tobypass supplemental fluid from the fluid return means through the otherbypass passage into the lower pressure circuit control passage,independent of said shiftable valve means.

3. A control system for a double acting fluid motor comprising: fluidsupply and fluid return means; means forming two circuit controlpassages connected respectively to opposite sides of said motor;shiftable valve means for selectively connecting either circuit controlpassage with the fluid supply means while connecting the other circuitcontrol passage with the fluid return means, and in one position forblocking flow of fluid to and from said circuit con-trol passages; meansopenly communicating with the fluid return means and forming twoseparate by-pass passages, each associated with and connectible to arespective one of said circuit control passage independent of theshiftable valve means; a valve interposed between and capable ofby-passing excess fluid from one circuit control passage into itsassociated by-pass passage in response to a predetermined pressuredifferential in those two passages when the shiftable valve means is inits flow blocking position; and a second valve interposed between andcapable of by-passing supplemental fluid from the other by-pass passageinto its associated circuit control passage when pressure in the latterdrops below pressure in the said other by-pass passage and in theconnected fluid return means.

4. A pressure fluid control system for a double acting fluid motorcomprising: fluid supply and return means; means forming two circuitcontrol passages connected respectively to opposite sides of said motor;shiftable valve means for selectively connecting either circuit controlpassage with the fluid supply means while simultaneously connecting theother circuit control passage with the fluid return means, and in oneposition for blocking flow of fluid to and from both said circuitcontrol passages; a separate by-pass passage between each circuitcontrol passage and the fluid return means; a directional valve in eachof said by-pass passages, each valve shiftable in response todifferential pressure, one oriented to aflord flow of fluid from itsassociated circuit control passage into its associated by-pass passageand to the fluid return means, and the other oriented to aflord fluidflow from the fluid return means through its associated by-pass passageinto its associated circuit control passage.

5. The system described in claim 4 in which the said one directionalvalve is of the relief type and opens only at a pressure in excess ofthat norm-ally supplied by the fluid supply means, and the said otherdirectional valve is a simple check valve.

6. A valve for controlling the flow of fluid to and from both ends of a.double-acting hydraulic. working cylinder". or motor comprising: a.housing having a bore. therein; fluid pressure supply and fluid return.means. defined? by thehousing, for connection with a. source offluidrunder; pressure and with. a reservoir, respectively,bothcthefluid: supply andreturn means communicating with. said bore;

means in the housing defining two circuit controlpassages forconnection: respectively to opposite endsofisaid; motor, bothsaidpassages communicating with said: bore; shiftable valvemeansinsaidbore eflective in one: position to block flow of fluid to andfrom both. circuit control: passages, and shiftable to selectivelyconnect either: circuit control passage withthe fluid supply meanswhile.

simultaneously connecting the other circuit control pas sage with thefluid return means; means in the housing: defining by-pass passages inopen communication with the fluid return means and respectivelyconnecting the. circuit control passages with said fluid. return means;a directionalvalve in each by-pass passage openable in response todifferential pressure, one oriented to. aflord' flow offluid from itsassociated control passage into its associated by-pass passage inresponse to a pressure in. that control passage greater than thepressure required to operate the motor under a loaded condition, theother directional valve being oriented to aflord fluid flow from.

the fluid return means into its associated circuit control passage inresponse to the slightest excess of pressure in the fluid return means.

7. The valve described in claim 6 in which each of said by-pass passagesis closely associated with a respective one of said circuit controlpassages, and is capable of connecting its associated control passagewith the fluid return means independent of the bore and the shiftablevalve means therein, through the opening of its respective directionalvalve.

8. A valve for controlling the flow of fluid to and from both ends of adouble acting hydraulic working cylinder or motor comprising: a housinghaving a valve spool receiving bore therein; a pressure fluid inletpassage in said housing in communication with said bore and connectibleto a source of fluid under high pressure; a fluid outlet passage in thehousing in communication with said bore and connectible to a reservoir;a pair of circuit control passages in communication with said bore forcom nection to the respective opposite ends of the cylinder; acannelured flow controlling valve spool reciprocable in said bore,effective in a neutral position to block the flow of fluid from theinlet to both circuit control passages and to block flow from bothcircuit control passages into said outlet through the bore, said spoolbeing shiftable to selectively connect either circuit control passagewith the inlet while simultaneously connecting the other circuit controlpassage with the outlet; a circuit relief bypass passage in opencommunication with the outlet and in valve controlled communication withone of said circuit control passages independent of said valve spool; a

pressure opened circuit relief valve interposed between the circuitrelief passage and its connected circuit control passage and oriented toby-pass fluid from the control passage into the circuit relief passagein response'to a 7 pressure increase in the said control passage to avalue greater than the pressure supplied by the inlet; an anticavitationby-pass passage in open communication with the outlet and in valvecontrolled communication with the other circuit control passageindependent of said valve spool; and a check valve interposed betweenthe anti-cavitation passage and the said other circuit control passageand affording flow of fluid from the former into passage in thehousingfor connection'to a sourceof high pressure liquid; a liquidreturn passage in the housing for connection to a liquid reservoir; acircuit relief by-pass passage in the housing; an anti-cavitationby-pass passage in the housing; a pair of circuit control passages inthe housing; two motor ports communicating respectively with saidcircuit control passages and constituting means to connect the valvewith the opposite ends of a double acting hydraulic hoisting cylinder,all said passages communicating with said bore, said by-pass passagesboth being in open communication with the liquid return passage, eachby-pass passage being connectible directly with a respective one of saidcircuit control passages through said bore and also at a location spacedfrom said bore, said circuit control passages being connectibleselectively with said pressure passage and with said liquid returnpassage through said bore; a cannelured liquid flow controlling valvespool reciprocable in said bore and movable to a neutral position inwhich liquid flow from both circuit control passages through the boreand to the return passage is blocked, and in which flow from thepressure passage into both circuit control passages is blocked; acircuit relief valve interposed between cavitation passage and in theconnected liquid return;

passage.

References Cited in the file of this patent UNITED STATES PATENTS1,807,191 Boyle May 26, 1931 1,807,231 Weeks May 26, 1931 2,193,736Onions Mar. 12, 1940 2,387,777 Stanton et al. Oct. 30, 1945 l 2,742,880Ball Apr. 24, 1956 2,755,741 Erskine July 24, 1956 2,783,742 Shafer Mar.5, 1957

